Question

Which of the following are examples of endothermic reactions?

• A. Combustion of methane
• B. Decomposition of water
• C. Dehydrogenation of ethane to the ethylene
• D. Conversion of graphite to diamond

Answer 1

Answer: (B), (C), (D)

The correct options are
B Decomposition of water
C Conversion of graphite to diamond
D Dehydrogenation of ethane to the ethylene

A) Combustion is always an exothermic process.
B) Decomposition of water requires energy. Hence it is endothermic.
C) Dehydrogenation is an endothermic reaction since energy is required to break the $C-H$ bonds to convert ethane to ethylene.
D) Graphite is more stable than diamond and energy is needed to convert graphite into diamond. The extra energy that has to be provided ends up in the tetrahedral structure of diamond.
Hence options B,C and D are the right answer.